Carbon nanotube dispersion, method for producing the same, electrode slurry composition containing the same, electrode containing the same, and secondary battery containing the same

Abstract

The present disclosure relates to a carbon nanotube dispersion containing carbon nanotubes, a first dispersant having an amide group, a second dispersant having at least one functional group selected from the group consisting of a hydroxyl group and a carboxyl group, and sulfur. The present disclosure also relates to a method for producing the dispersion, an electrode slurry composition containing the dispersion, an electrode containing the electrode slurry composition, and a secondary battery containing the electrode.

Description

[Technical Field]

[0001] This application claims priority based on Korean Patent Application No. 10-2022-0112212, filed on September 5, 2022, the contents of which are incorporated herein by reference.

[0002] This disclosure relates to a carbon nanotube dispersion, a method for producing the same, an electrode slurry composition containing the same, an electrode containing the same, and a secondary battery containing the same. [Background technology]

[0003] A secondary battery is a battery that can be used repeatedly through a discharge process that converts chemical energy into electrical energy, and a charging process that is the reverse of the discharge process. A secondary battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. Generally, each of the positive and negative electrodes consists of an electrode current collector and an electrode active material layer formed on the electrode current collector. The electrode active material layer is formed by coating an electrode slurry composition containing electrode active material, a conductive material, and a binder onto the electrode current collector, and then drying and rolling it.

[0004] Conductive materials are used to improve the conductivity of electrode active materials. Traditionally, spherical conductive materials such as carbon black have been used. However, because spherical conductive materials did not show a significant effect in improving electrical conductivity, an excessive amount of conductive material was used to obtain a sufficient effect, which reduced the amount of electrode active material in the electrode and led to a decrease in battery capacity.

[0005] To overcome these problems, attempts are being actively made to use carbon nanotubes (CNTs), which have high conductivity, as a conductive material. Even a small amount of carbon nanotubes can provide good conductivity, and by using carbon nanotubes, the amount of conductive material used in battery electrodes is significantly reduced compared to when carbon black is used, thereby increasing the electrical capacity of the battery.

[0006] In order to use carbon nanotubes as a negative electrode conductive material, it is necessary to prepare an aqueous dispersion with low viscosity from the perspective of processability.

[0007] Polyvinylpyrrolidone (PVP), a dispersant having an amide group, is a polymer surfactant. PVP is known to be used as a dispersant, emulsifier, thickener, etc. in various dispersion systems and to be effective for the dispersion of carbon nanotubes (Patent Document 1).

[0008] Also, polyacrylic acid and tannic acid containing a carboxyl group are known to be effective for the dispersion of carbon nanotubes.

[0009] Summarizing the above-known information, it is presumed that when polyvinylpyrrolidone and polyacid are used in combination, a better CNT dispersion effect can be obtained. However, in reality, when these materials are mixed, usually, the bond between the two materials becomes excessively strong, resulting in the formation of insoluble matter or aggregates, and the dispersibility of the dispersion decreases.

Prior Art Documents

Patent Documents

[0010]

Patent Document 1

Non-Patent Documents

[0011]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0012] The present disclosure relates to a carbon nanotube dispersion with improved dispersibility, a method for producing the same, an electrode slurry composition containing the same, an electrode containing the same, and a secondary battery containing the same.

Means for Solving the Problems

[0013] One embodiment of the present disclosure provides a carbon nanotube dispersion comprising: carbon nanotubes; a first dispersant containing an amide group; a second dispersant containing at least one functional group selected from the group consisting of a hydroxyl group and a carboxyl group; and sulfur.

[0014] Another embodiment of the present disclosure provides a method for producing the above carbon nanotube dispersion, the method comprising mixing carbon nanotubes, a first dispersant containing an amide group, and a second dispersant containing at least one functional group selected from the group consisting of a hydroxyl group and a carboxyl group.

[0015] A further embodiment of the present disclosure provides an electrode slurry composition comprising the above carbon nanotube dispersion, a silicon-based electrode active material, and a binder.

[0016] A further embodiment of the present disclosure provides an electrode comprising an electrode active material layer made from the above electrode slurry composition.

[0017] A further embodiment of the present disclosure provides a secondary battery comprising the above electrode. [[Effect of the Invention]]

[0018] The carbon nanotube dispersion according to one embodiment of the present disclosure has a significantly low viscosity and improved carbon nanotube dispersibility.

[0019] The carbon nanotube dispersion according to one embodiment of the present disclosure has excellent coating characteristics and processability when used in electrode manufacturing. [[Brief Description of the Drawings]]

[0020] [Figure 1] FIG. 1 shows the experimental results of Experimental Example 1; [Figure 2-4]Figures 2 to 4 show the results of confirming whether sulfur was present in the first dispersant used in the examples and comparative examples. [Modes for carrying out the invention]

[0021] The details of this disclosure are described below.

[0022] A carbon nanotube dispersion according to one embodiment of the present disclosure is a dispersion containing carbon nanotubes. Specifically, a carbon nanotube dispersion refers to a system in which carbon nanotubes are dispersed in a dispersant and do not aggregate.

[0023] One embodiment of the present disclosure provides a carbon nanotube dispersion containing carbon nanotubes; a first dispersant containing an amide group; a second dispersant containing at least one functional group selected from the group consisting of hydroxyl groups and carboxyl groups; and sulfur.

[0024] Conventionally, a first dispersant containing an amide group has been known to be effective in dispersing carbon nanotubes (Patent Document 1), and a second dispersant containing at least one functional group selected from the group consisting of hydroxyl groups and carboxyl groups has the effect of reducing the viscosity of the dispersion due to the influence of the functional group (Non-Patent Document 1).

[0025] Furthermore, the oxygen atoms of the amide groups in the first dispersant and the functional groups (hydroxyl or carboxyl groups) in the second dispersant form hydrogen bonds with each other, contributing to a decrease in the viscosity of the dispersion. However, this strong hydrogen bonding can lead to the formation of insoluble matter or aggregates (compounds). In this case, there are many constraints on the selection of dispersants. For example, it may be necessary to control the respective content of the first and second dispersants, or to use only specific types of dispersants as the first and / or second dispersants.

[0026] The inventors have completed this disclosure by discovering that the aggregation problem between the first and second dispersants is mitigated when the dispersion contains elemental sulfur. In such cases, the viscosity of the dispersion is low, even if carbon nanotubes with a large specific surface area are included in the dispersion. The effect of mitigating aggregation can be confirmed by visual observation after storing the carbon nanotube dispersion for a certain period of time.

[0027] A carbon nanotube dispersion according to one embodiment of the present disclosure contains carbon nanotubes with excellent conductivity and dispersibility so as to minimize aggregation of carbon nanotubes. This property can be confirmed by the remarkably low viscosity of the dispersion.

[0028] A carbon nanotube dispersion according to one embodiment of the present disclosure is characterized by containing sulfur. Sulfur may be present in the dispersion in compound form, elemental form, or ionic form. For example, sulfur may originate from sulfur-containing compounds, which will be described later. The presence and content of sulfur can be confirmed by elemental analysis.

[0029] In one embodiment of this disclosure, the sulfur content in the carbon nanotube dispersion may be 0.01 to 10% by weight, 0.05 to 8% by weight, or 0.1 to 5% by weight on a solids basis. The range of sulfur element content can be satisfied by controlling the content of sulfur-containing compounds. The sulfur element content can be measured and calculated using an elemental analyzer (EA), the details of which will be described later.

[0030] In one embodiment of this disclosure, the sulfur content may be 0.01 to 20%, 0.1 to 10%, or 1 to 5% relative to the total oxygen (O) and nitrogen (N) content on a solids basis. When the above numerical ranges are met, the ratio of the total oxygen and nitrogen content to the sulfur content involved in hydrogen bonding is controlled, preventing aggregation of dispersants and improving the dispersibility of carbon nanotubes. The content of each element can be measured and calculated using an elemental analyzer (EA), the details of which will be described later.

[0031] In one embodiment of the present disclosure, part or all of the first dispersant may be sulfur-substituted. If part of the first dispersant is sulfur-substituted, the remaining part of the first dispersant may consist of a sulfur-unsubstituted substance. For example, the first dispersant may consist of a sulfur-substituted portion and a non-sulfur-substituted portion.

[0032] In one embodiment of the present disclosure, the sulfur substitution ratio of the first dispersant may be 10 to 100 mol%, 20 to 80 mol%, or 40 to 60 mol%.

[0033] In one embodiment of the present disclosure, the first dispersant has a Fourier transform infrared (FTIR) spectrum of 1,110 cm⁻¹. -1 ~1,050cm -1 The first peak, 1,140 cm -1 ~1,180cm -1 The second peak, and 1,180 cm -1 ~1,220cm -1 The matrix may show at least one peak selected from the group consisting of the third peak. The first to third peaks indicate the presence of S=O bonds in the dispersant, and the presence of these peaks confirms that the first dispersant is substituted with sulfur.

[0034] In one embodiment of this disclosure, since the first dispersant has an amide group, the first dispersant can form a hydrogen bond with the hydroxyl group or carboxyl group of the second dispersant, which will be described later.

[0035] In one embodiment of the present disclosure, the first dispersant may be polyvinylpyrrolidone, polyesteramide, polycarboxylamide, polyamidoamine, thioamidoamine, water-soluble nylon, or a combination thereof. Since the first dispersant has an amide group, the first dispersant improves viscosity and suppresses changes in viscosity over time.

[0036] In one embodiment of this disclosure, the first dispersant may have a weight-average molecular weight of 1,000 to 100,000 g / mol, preferably 2,000 to 80,000 g / mol, more preferably 2,000 to 30,000 g / mol, and even more preferably 2,000 to 15,000 g / mol. If the weight-average molecular weight of the first dispersant is less than 1,000 g / mol, the dispersibility of carbon nanotubes will decrease, and a problem may occur in which the first dispersant dissolves during electrode manufacturing. On the other hand, if the weight-average molecular weight exceeds 100,000 g / mol, the viscosity of the carbon nanotube dispersion will increase, and the coatability and processability may deteriorate. Therefore, it is preferable that the weight-average molecular weight of the first dispersant be within the above numerical range.

[0037] In one embodiment of the present disclosure, the second dispersant has a hydroxyl group or a carboxyl group, so that the second dispersant can form a hydrogen bond with the amide group of the first dispersant described above.

[0038] In one embodiment of the present disclosure, the second dispersant may contain an aromatic ring. In this case, the complex structure of the second dispersant can effectively reduce the viscosity of the dispersion.

[0039] In one embodiment of the present disclosure, the second dispersant may comprise two or more aromatic rings. For example, the second dispersant may be one or more types selected from the group consisting of baicalin, luteolin, taxifolin, myricetin, quercetin, rutin, catechin, epigallocatechin gallate, butein, piceatenol, and tannic acid. Preferably, the second dispersant may be tannic acid, quercetin, epigallocatechin gallate, or a combination thereof.

[0040] In one embodiment of the present disclosure, the second dispersant may be a phenol compound. In the phenol compound, one or more aromatic rings may have one or more structures selected from the group consisting of a phenol structure, a catechol structure, a gallol structure, and a naphthol structure. A phenol structure is a structure in which one hydroxyl group is bonded to a benzene ring, a catechol structure is a structure in which two hydroxyl groups are bonded to a benzene ring, a gallol structure is a structure in which three hydroxyl groups are bonded to a benzene ring, and a naphthol structure is a structure in which one hydroxyl group is bonded to naphthalene.

[0041] In one embodiment of the present disclosure, the second dispersant may be a polyacrylic acid compound. The polyacrylic acid compound is an acrylic acid compound containing two or more acidic hydrogen atoms.

[0042] In one embodiment of this disclosure, the polyacrylic acid compound may be polyacrylic acid (PAA) or a polyacrylic acid derivative. The polyacrylic acid derivative may be polyacrylic acid-co-maleic acid (PAAMA).

[0043] In one embodiment of the present disclosure, the second dispersant may include a compound containing an aromatic ring, a polyacrylic acid compound, or a combination thereof. The compounds containing aromatic rings and polyacrylic acid compounds are as described above.

[0044] In one embodiment of this disclosure, the weight ratio of the first dispersant to the second dispersant may be 1:10 to 10:1, 1:5 to 5:1, or 1:1 to 1:5. When the above range is satisfied, the effect of dispersing carbon nanotubes is improved and the viscosity of the dispersion is maintained at a low level.

[0045] In one embodiment of the present disclosure, the content of the first dispersant may be in the range of 0.01 to 10% by weight, 0.01 to 5% by weight, or 0.1 to 3% by weight, based on the total weight of the dispersion.

[0046] In one embodiment of the present disclosure, the content of the second dispersant may be in the range of 0.01 to 10% by weight, 0.01 to 5% by weight, or 0.1 to 3% by weight based on the total weight of the dispersion liquid.

[0047] In one embodiment of the present disclosure, carbon nanotubes are used to improve the conductivity of the electrode. Carbon nanotubes are formed by shaping a graphite sheet into a cylindrical shape with a nanoscale diameter. Carbon nanotubes have a sp 2 bonding structure. Depending on the angle at which the graphite sheet is wound and the structure of the graphite sheet, carbon nanotubes may have conductivity or semiconductor properties. Carbon nanotubes can be classified into single-walled carbon nanotubes (SWCNT), double-walled carbon nanotubes (DWCNT), and multi-walled carbon nanotubes (MWCNT) according to the number of bonds forming the wall. These carbon nanotubes can be appropriately selected according to the purpose of the dispersion liquid. Furthermore, carbon nanotubes may aggregate or form a two-dimensional shape in which they are arranged two-dimensionally. For example, carbon nanotubes are regularly arranged in a specific direction to form a bundle or rope shape. Alternatively, carbon nanotubes are irregularly arranged in many directions and intertwined to form an intertwined spherical or potato shape.

[0048] In one embodiment of the present disclosure, the carbon nanotubes may be single-walled carbon nanotubes (SWCNT) or multi-walled carbon nanotubes (MWCNT).

[0049] In one embodiment of the present disclosure, the BET specific surface area of the carbon nanotubes is 10 to 5,000 m 2 / g, preferably 30 to 3,000 m 2 / g, more preferably 50 to 2,000 m 2 / g. When the above numerical range is satisfied, the effect of enhancing conductivity is excellent. The BET specific surface area of carbon nanotubes may vary depending on the type of carbon nanotubes.

[0050] In one embodiment of this disclosure, the BET specific surface area of ​​the single-walled carbon nanotube is 800 to 5,000 m². 2 / g, preferably 800-3,000m 2 / g, more preferably 900~2,000m 2 The range of / g is also acceptable. When the above numerical range is met, it has an excellent effect in improving conductivity.

[0051] In one embodiment of this disclosure, the BET specific surface area of ​​the multi-walled carbon nanotube is 10 to 1,200 m². 2 / g, preferably 30-1,000m 2 / g, more preferably 50-800m 2 The range of / g is also acceptable. When the above numerical range is met, it has an excellent effect in improving conductivity.

[0052] In one embodiment of the present disclosure, the carbon nanotube content may be in the range of 0.01 to 10% by weight, preferably 0.1 to 8% by weight, based on the total weight of the carbon nanotube dispersion. The carbon nanotube content can be appropriately adjusted depending on the specific surface area of ​​the carbon nanotubes used. For example, 800 m 2 When using carbon nanotubes with a specific surface area of ​​1 / g or more, the carbon nanotube content may be in the range of 0.01 to 5% by weight, preferably 0.01 to 3% by weight, and more preferably 0.01 to 2% by weight, based on the total weight of the carbon nanotube dispersion. If the specific surface area and content of carbon nanotubes are outside the above range, problems arise such as increased process costs due to reduced load during electrode manufacturing, decreased adhesion due to binder migration during electrode drying, and increased viscosity of the carbon nanotube dispersion.

[0053] In one embodiment of the present disclosure, the carbon nanotube may be composed of two or more carbon nanotube units. The carbon nanotube unit is formed by shaping a graphite sheet into a cylindrical shape having a nanoscale diameter, sp 2 It may have a bonding structure.

[0054] In one embodiment of this disclosure, the diameter of the carbon nanotube unit may be in the range of 1 to 200 nm, 1 to 150 nm, or 1 to 100 nm. When the above numerical ranges are satisfied, the dispersibility of the carbon nanotubes is improved, and when the carbon nanotubes are applied to an electrode, an increase in the resistance of the electrode can be prevented.

[0055] In one embodiment of this disclosure, the length of the carbon nanotube unit may be in the range of 0.1 to 200 μm, 0.1 to 150 μm, or 0.5 to 100 μm. When the above numerical ranges are satisfied, the dispersibility of the carbon nanotubes is improved, and when the carbon nanotubes are applied to an electrode, an increase in the resistance of the electrode can be prevented.

[0056] In one embodiment of this disclosure, the aspect ratio (i.e., the ratio of length to diameter) of the carbon nanotube may be in the range of 5 to 50,000 or 10 to 15,000. When the above numerical range is satisfied, the dispersibility of the carbon nanotube is improved, and when the carbon nanotube is applied to an electrode, an increase in the resistance of the electrode can be prevented.

[0057] In one embodiment of this disclosure, the average particle size (D50) of the carbon nanotubes may be in the range of 0.1 to 20 μm, 0.5 to 1 μm, 1 to 5 μm, or 2 to 4 μm. The average particle size (D50) refers to the particle size value at 50% of the cumulative particle size distribution of the carbon nanotubes. The average particle size (D50) can be measured, for example, using laser diffraction. When the above range is satisfied, the carbon nanotubes do not aggregate with each other, and the dispersibility of the carbon nanotubes can be improved.

[0058] In one embodiment of this disclosure, the temperature is 25°C and the shear rate is 15 sec. -1The viscosity of the carbon nanotube dispersion may be 4,000 cPs or less, 3,000 cPs or less, 1,000 cPs or less, or 600 cPs or less. The lower limit of the viscosity range is not particularly limited, but the lower the viscosity, the better the dispersibility. However, considering the purpose of this disclosure, the viscosity may be 10 cPs or more, 30 cPs or more, or 50 cPs or more. When the above viscosity range is satisfied, the carbon nanotubes in the carbon nanotube dispersion do not aggregate with each other, and the processability when the carbon nanotube dispersion is used in electrode manufacturing is improved.

[0059] The viscosity of a carbon nanotube dispersion can be measured using methods commonly used in the technical field to which this technique belongs. For example, at 25°C and a shear rate of 15 sec. -1 This can be measured using a Brookfield DVNextCP Rheometer. For more accurate measurements, the prepared carbon nanotube dispersion may be stored at 25°C for one week before measurement.

[0060] In one embodiment of this disclosure, the value of the carbon nanotube dispersion calculated according to the following Equation 1 may be in the range of 2 to 10, 2 to 6.5, or 3 to 6. The calculated value in Equation 1 below is the shear thinning index of the dispersion. This index refers to the ratio of viscosities measured at different shear rates. When the above range is satisfied, it prevents a decrease in the fluidity of the dispersion due to an excessive increase in viscosity that occurs under static conditions, and enables uniform mixing during electrode manufacturing. In addition, the storage stability of the carbon nanotube dispersion is improved because sedimentation of carbon nanotube particles is prevented.

[0061] [Formula 1] Shear thinning index (STI) = V low / V high In equation 1 above, V low This is under conditions of 25°C and a shear rate of 15 sec. -1 This is the viscosity of the dispersion. V high This is under conditions of 25°C and a shear rate of 150 sec. -1This is the viscosity of the dispersion.

[0062] In one embodiment of this disclosure, the value calculated by the following Equation 2 for a carbon nanotube dispersion may be in the range of 1 to 5, 1 to 3, or 1.1 to 2. The calculated value of Equation 2 below shows the relationship between the shear thinning index (STI) characteristics of the dispersion and the average particle size of the carbon nanotubes contained in the dispersion. Generally, if the particle size (D50) of the carbon nanotubes is excessively small, the carbon nanotubes aggregate with each other, and the shear thinning index (STI) of the dispersion tends to increase. Also, if the particle size (D50) of the carbon nanotubes is excessively large, the carbon nanotubes are not sufficiently dispersed and form a network structure, and the overall viscosity and shear thinning index (STI) of the carbon nanotubes tend to increase.

[0063] However, in the carbon nanotube dispersion according to one embodiment of the present disclosure, the viscosity stability over time is improved even if the particle size of the carbon nanotubes is small, provided that the calculated value of Equation 2 is within the above numerical range.

[0064] [Formula 2] JPEG0007900870000001.jpg16160 In equation 2 above, STI is the shear thinning index of the dispersion. D50 is the average particle size of carbon nanotubes.

[0065] In one embodiment of the present disclosure, the carbon nanotube dispersion may contain an alkali metal element. Because the carbon nanotubes of the present disclosure contain an alkali metal element, the dispersibility of the materials contained in the dispersion may be improved. Specifically, the first dispersant and the second dispersant contained in the dispersion may form a complex with each other. These complexes have low solubility in solvents such as water, which can lead to an increase in the viscosity of the dispersion. However, the alkali metal element contained in the carbon nanotube dispersion of the present disclosure solves this problem by dissolving the complex.

[0066] In one embodiment of the present disclosure, the form of the alkali metal is not particularly limited, and the alkali metal may exist in the form of its alkali metal salt.

[0067] In one embodiment of the present disclosure, the concentration of the alkali metal element may be in the range of 1 to 300 ppm, 5 to 200 ppm, or 5 to 150 ppm in the carbon nanotube dispersion.

[0068] In one embodiment of the present disclosure, the carbon nanotube dispersion may contain at least one alkali metal salt selected from the group consisting of KOH, NaOH, K2CO3, Na2CO3, or LiCo3.

[0069] In one embodiment of this disclosure, when the first dispersant is a polyvinylpyrrolidone resin, the molar ratio of the alkali metal salt may be 60 moles or less, 30 moles or less, or 25 moles or less per 100 moles of vinylpyrrolidone monomer. The lower limit of the molar ratio is not particularly limited, but the molar ratio may be 0.1 moles or more, 1 mole or more, or 2 moles or more. When the above range is satisfied, the viscosity of the carbon nanotube dispersion is measured at 25°C and a shear rate of 15 sec. -1 It can be controlled to a range of 1,300 cPs or less.

[0070] The molar ratio of alkali metal salts can be calculated from the molecular weights of the alkali metal salt and the vinylidone monomer, as well as the respective content (weight %) of the alkali metal salt and polyvinylidone. Specifically, the value can be calculated using the following formula 3.

[0071] [Formula 3] Molar ratio of alkali metal salts = {(weight %) of alkali metal salt / (molecular weight of alkali metal salt)} / {(weight %) of polyvinylidone / (molecular weight of vinylidone monomer)} * 100

[0072] For example, if the content of polyvinylpyrrolidone and alkali metal salt (LiOH) is in the range of 0.6% by weight and 0.01% by weight, respectively, based on the total weight of the dispersion, and the molecular weight of the alkali metal salt (LiOH) is 24 g / mol and the molecular weight of vinylidone monomer is 111.14 g / mol, then the molar ratio of the alkali metal salt is calculated to be 7.7 moles per 100 moles of vinylpyrrolidone monomer [7.7 = {(0.01) / (24)} / {(0.6) / (111.14)} * 100].

[0073] A vinylpyrrolidone monomer refers to a five-membered lactam ring bonded to a vinyl group, and is a unit that constitutes polyvinylpyrrolidone resins. Specifically, the vinylpyrrolidone monomer may be the monomer represented by chemical formula 2 in polyvinylpyrrolidone represented by chemical formula 1.

[0074] [ka]

[0075] [ka]

[0076] In one embodiment of the present disclosure, the carbon nanotube dispersion may further contain a solvent. The solvent is used to pre-disperse the carbon nanotubes and supply them as a carbon nanotube dispersion to prevent aggregation of carbon nanotubes that may occur when the carbon nanotubes are directly mixed with the electrode active material to prepare an electrode slurry composition.

[0077] In one embodiment of this disclosure, the solvent may be an aqueous solvent. For example, the aqueous solvent may be water. When water is used as the solvent, it is easier to control the viscosity of the dispersion and does not generate toxic substances.

[0078] Another embodiment of the present disclosure relates to a method for producing a carbon nanotube dispersion, comprising mixing carbon nanotubes, a first dispersant comprising an amide group, and a second dispersant comprising at least one functional group selected from the group consisting of hydroxyl groups and carboxyl groups.

[0079] In one embodiment of the present disclosure, the step of mixing carbon nanotubes, a first dispersant containing an amide group, and a second dispersant containing at least one functional group selected from the group consisting of hydroxyl and carboxyl groups may be carried out under temperature conditions in which the physical properties do not change. For example, this step may be carried out at a temperature of 50°C or less, more specifically in the temperature range of 5°C to 50°C.

[0080] In one embodiment of the present disclosure, the step of dispersing carbon nanotubes in a dispersion may be carried out by a milling method using a ball mill, bead mill, disc mill, basket mill, or high-pressure homogenizer, more specifically by a milling method using a disc mill or high-pressure homogenizer.

[0081] When using a disc mill, the bead size can be appropriately determined depending on the type and amount of carbon nanotubes and the type of dispersant. Specifically, the bead diameter may be in the range of 0.1 to 5 mm, more specifically 0.5 to 4 mm. Furthermore, bead milling may be performed at a speed of 2,000 to 10,000 rpm, more specifically 5,000 to 9,000 rpm.

[0082] When milling using a high-pressure homogenizer, the plunger pump pushes the mixture through the gap in the homogenizing valve, subjecting the mixture to cavitation, shear, shock, explosion, and other phenomena as it passes through the gap.

[0083] In one embodiment of the present disclosure, the step of dispersing carbon nanotubes in a dispersion may be carried out for 10 to 120 minutes, more specifically 20 to 90 minutes, so that the carbon nanotubes are sufficiently dispersed.

[0084] A further embodiment of the present disclosure relates to an electrode slurry composition comprising the above carbon nanotube dispersion, electrode active material, and binder.

[0085] In one embodiment of the present disclosure, the electrode active material includes a silicon-based electrode active material. The silicon-based electrode active material may include at least one selected from the group consisting of metallic silicon (Si), silicon oxide (SiOx, where 0 < x < 2), silicon carbide (SiC), and Si-Y alloy (where Y is an element selected from the group consisting of alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements, transition metals, rare earth elements, and combinations thereof, but does not include Si in the examples of silicon-based electrode active materials). The element Y may be selected from the group consisting of Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Ti, Ge, P, As, Sb, Bi, S, Se, Te, Po, and combinations thereof.

[0086] The silicon-based electrode active material exhibits higher capacity characteristics than the carbon-based electrode active material. Therefore, when such a silicon-based electrode active material is used, better capacity characteristics can be obtained. However, since the silicon-based electrode active material shows a large volume change during charge and discharge, the battery characteristics rapidly deteriorate as the battery is repeatedly charged and discharged. This deteriorates the cycle characteristics and hinders the commercialization of the battery using this material. However, when carbon nanotubes are used as a conductive material as in the present disclosure, the cycle characteristics can be improved even when a silicon-based electrode active material is used. Therefore, by using the electrode slurry composition of the present disclosure including the carbon nanotube dispersion of the present disclosure and the silicon-based electrode active material, a secondary battery having excellent cycle characteristics and capacity characteristics can be realized.

[0087] In one embodiment of the present disclosure, the electrode slurry composition may further contain other types of electrode active materials in addition to silicon-based electrode active materials. Examples of additional electrode active materials include carbon materials such as artificial graphite, natural graphite, graphitized carbon fibers, and amorphous carbon; metal compounds such as Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, and Al alloys that can be alloyed with lithium; metal oxides such as SnO2, vanadium oxide, and lithium vanadium oxide that can be doped and dedoped with lithium; and composite materials such as Sn-C composites containing metal compounds and carbon materials. Among these examples, carbon materials are particularly preferred.

[0088] In one embodiment of this disclosure, the total amount of electrode active material, which is a combination of silicon-based electrode active material and other types of electrode active material, may be in the range of 70 to 99% by weight, preferably 80 to 98% by weight, relative to the total solid content of the electrode slurry composition. When the content of electrode active material satisfies the above range, excellent capacity characteristics can be obtained.

[0089] In one embodiment of the present disclosure, a binder is used to ensure adhesion between active materials or between active materials and current collectors. Any binder commonly used in the art may be used as the binder, and the type is not particularly limited. For example, the binder may be polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluorinated rubber, or one or more of these various copolymers.

[0090] In one embodiment of the present disclosure, the binder may be present in an amount of 5% by weight or less, preferably 1 to 3% by weight, based on the total solid content of the electrode slurry composition. When the binder content is within the above range, the increase in electrode resistance is minimized and excellent electrode adhesion can be obtained.

[0091] In one embodiment of the present disclosure, the electrode slurry composition may further contain a solvent for viscosity control as needed. In this case, the solvent may be water, an organic solvent, or a mixture thereof. Examples of organic solvents include amide-type polar organic solvents such as dimethylformamide (DMF), diethylformamide, dimethylacetamide (DMAc), and N-methylpyrrolidone (NMP); alcohols such as methanol, ethanol, 1-propanol, 2-propanol (isopropyl alcohol), 1-butanol (n-butanol), 2-methyl-1-propanol (isobutanol), 2-butanol (sec-butanol), 1-methyl-2-propanol (tert-butanol), pentanol, hexanol, heptanol, or octanol; glycols such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, 1,3-propanediol, 1,3-butanediol, 1,5-pentanediol, and hexylene glycol; and glycerin and trimethylol glycol. Examples include polyhydric alcohols such as pan, pentaerythritol, and sorbitol; glycol ethers such as ethylene glycol monomethyl ether, diethylene glycol monomethyl ether, triethylene glycol monomethyl ether, tetraethylene glycol monomethyl ether, ethylene glycol monoethyl ether, diethylene glycol monoethyl ether, triethylene glycol monoethyl ether, tetraethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, and tetraethylene glycol monobutyl ether; ketones such as acetone, methyl ethyl ketone, methyl propyl ketone, and cyclopentanone; and esters such as ethyl acetic acid, γ-butyrolactone, and β-propiolactone. Each of the exemplary materials can be used alone as a solvent, or a combination of two or more exemplary materials can be used. However, the solvent is not limited to these examples.

[0092] In one embodiment of the present disclosure, the electrode slurry composition may further contain additives such as viscosity modifiers and fillers, as needed.

[0093] In one embodiment of the present disclosure, an electrode is provided comprising an electrode active material layer formed from the above-described electrode slurry composition. Specifically, the electrode can be manufactured by applying the above-described electrode slurry composition of the present disclosure and drying it to form an electrode active material layer. More specifically, the electrode active material layer can be formed by applying the electrode slurry composition onto an electrode current collector and then drying it. Alternatively, the electrode active material layer can be formed by applying the electrode slurry composition onto a support, peeling the resulting film from the support, and laminating the film onto an electrode current collector. After the electrode active material layer is formed in this manner, a rolling process can be additionally performed as needed. In this case, the drying and rolling processes can be carried out under appropriate conditions considering the physical properties of the final manufactured electrode.

[0094] In one embodiment of the present disclosure, the material of the electrode current collector is not particularly limited, as long as it is conductive and does not cause chemical changes within the battery cell. For example, any material selected from copper, stainless steel, aluminum, nickel, titanium, or alloys thereof can be used. Alternatively, a material surface-treated with carbon, nickel, titanium, or silver, or calcined carbon can be used.

[0095] In one embodiment of this disclosure, the electrode current collector may have a thickness of 3 to 500 μm, and the bonding between the electrode active material layer and the electrode current collector can be strengthened by forming fine irregularities on the surface of the electrode current collector. The electrode current collector can be provided in any form. For example, the electrode current collector can take the form of a film, sheet, foil, mesh, porous material, foam, or nonwoven fabric.

[0096] In one embodiment of this disclosure, the electrode may be a negative electrode.

[0097] One embodiment of the present disclosure provides a secondary battery including the above-described electrodes.

[0098] One embodiment of the present disclosure provides a secondary battery comprising a positive electrode; a negative electrode; and a separator and electrolyte inserted between the positive and negative electrodes, wherein at least one of the positive and negative electrodes is the aforementioned electrode.

[0099] In one embodiment of this disclosure, the secondary battery may be a lithium secondary battery.

[0100] In one embodiment of this disclosure, the separator isolates the negative and positive electrodes from each other and provides a passage for the movement of lithium ions. The separator that can be used in a secondary battery is not particularly limited. Specifically, a porous polymer film made of a polyolefin polymer such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, or ethylene / methacrylate copolymer can be used as the separator. Alternatively, a laminate of two or more layers made of the above exemplary materials can be used as the separator. Furthermore, conventional porous nonwoven fabric members made of high-melting-point glass fibers or polyethylene terephthalate fibers can also be used as the separator. Moreover, a coated separator containing ceramic components or polymer materials can be used to obtain good heat resistance and mechanical strength, and this separator may have a single-layer or multi-layer structure.

[0101] In one embodiment of the present disclosure, the electrolyte can be selected from organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, inorganic solid electrolytes, and inorganic molten electrolytes that can be used in secondary batteries, but the type of electrolyte is not limited to these. [Examples]

[0102] The present disclosure will be described in more detail below with reference to the embodiments described herein.

[0103] <Preparation of carbon nanotubes> Prepare the carbon nanotubes shown below.

[0104] - CNT-1 (Single-walled carbon nanotube; manufactured by OCSiA; product name 01RW03; specific surface area > 800 m²) 2 (Average diameter of each unit = 2nm) - CNT-2 (Multilayer carbon nanotube; manufactured by JEIO; product name 6A; specific surface area = 643 m²) 2 (Average diameter of each unit = 9-10 nm) - CNT-3 (Multilayer carbon nanotube; manufactured by LG CHEM; product name BT1003M; specific surface area = 186 m²) 2 (Average diameter of each unit = 13 nm)

[0105] <Preparation of the first dispersant> Ar gas was added to the reactor to stabilize the atmosphere. A mixed solution of monomer N-vinylpyrrolidone and potassium sulfite was prepared by dissolving them in water. The mixed solution was stirred and reacted under an Ar atmosphere at 40°C for 24 hours, and then slowly cooled to room temperature. A certain amount of water was evaporated from the mixed solution to prepare a concentrate. The concentrate was precipitated with acetone, filtered, and dried to produce PVP-1 containing sulfur (S).

[0106] PVP-2 purchased from Aldrich and PVP-3 purchased from Ashland were prepared as sulfur-free dispersants.

[0107] Attenuated total internal reflection (ATR) was used to confirm the presence of sulfur in the first dispersant. PVP-1 was measured at 1,030 cm⁻¹. -1 , 1,160cm -1 , and 1,200cm -1 A peak was observed at the same position (Figure 2), but PVP-2 (Figure 3) and PVP-3 (Figure 4) did not show peaks at the same position. From the above results, it was confirmed that PVP-1, as the first dispersant, contains sulfur.

[0108] <Preparation of the second dispersant> Tannic acid (TA) purchased from Aldrich and polyacrylic acid (PAA, weight-average molecular weight 2,000) purchased from Thermo Scientific were prepared.

[0109] <Preparation of dispersion> Example 1 A carbon nanotube dispersion was prepared by mixing 0.4 wt% CNT-1 as a carbon nanotube, 0.48 wt% PVP-1 as a first dispersant, 0.12 wt% TA as a second dispersant, and 99 wt% distilled water as a solvent, and then mixing the mixture in a high-pressure homogenizer.

[0110] Examples and Comparative Examples As other examples and comparative examples, dispersions were prepared by varying the weight and type of each material, as shown in Table 1 below. The physical properties of each dispersion were analyzed.

[0111] The composition of each dispersion prepared in the examples and comparative examples, and the results of each experiment are summarized in Table 1 below. The content of each component is based on the total weight of the dispersion.

[0112] Experimental Example 1: Observation of Dispersant Aggregation Test solutions were prepared in the same manner as in the above examples and comparative examples, except that carbon nanotubes were not added. Each test solution was mixed at room temperature using a vortex mixer and left to stand for 6 hours to observe aggregation and precipitation.

[0113] The test solutions of Example 4 and Example 1 did not show aggregation and precipitation, but the test solution of Comparative Example 1 did show aggregation and precipitation (Figure 1).

[0114] Experimental Example 2: Viscosity Measurement Using a Brookfield DVNextCP Rheometer, measurements were taken at 25°C and a shear rate of 2.5 sec. -1 and 15sec -1 The viscosity was measured.

[0115] Experimental Example 3: Calculation of Average Particle Size A commercially available laser diffraction particle size analyzer (Malvern Mastersizer3000) was used for laser diffraction. Using this instrument, the average particle size (D50) at 50% of the particle size distribution was calculated. D10 and D90 represent the particle sizes at 10% and 90% of the particle size distribution, respectively.

[0116] Experimental Example 4: Measurement of Sulfur Content - Sample preparation The dispersions prepared in the examples and comparative examples were dried in a 90°C convection oven for 3 days, and then powder samples were prepared using a mixer grinder.

[0117] -- Measurement of sulfur content An elemental analyzer (EA) was used for the measurement.

[0118] Organic samples were oxidized to CO2, H2O, NO2, and SO2 at high temperatures (approximately 1,000°C) using a catalyst, and the resulting gases were separated using a GC column (packed column). Detection was performed using a thermal conduction detector (TCD), and calibration curves were prepared in advance using standard substances for each of C, H, N, and S. The content of each element was quantified in % from the GC chromatogram.

[0119] [Table 1] JPEG0007900870000005.jpg230155JPEG0007900870000006.jpg149161

[0120] From the results above, it was confirmed that when sulfur was not present (Comparative Examples 1-4), the viscosity of each dispersion increased significantly. In other words, the first and second dispersants agglomerated, increasing the viscosity of the dispersion.

[0121] The dispersant in Example 1 contains a first dispersant and a second dispersant that can form hydrogen bonds with each other. However, the first dispersant is substituted with sulfur, which inhibits hydrogen bonding between the first and second dispersants, resulting in less aggregation between the first and second dispersants. On the other hand, the dispersions in Comparative Examples 1 and 2 were the same as the dispersion in Example 1, except that the first dispersant used PVP that was not substituted with sulfur. This resulted in a problem where many hydrogen bonds formed between the first and second dispersants, and the viscosity of the dispersion increased by more than 10 times.

[0122] The dispersion in Comparative Example 3 was identical to the dispersion in Example 5, except that PVP-2 was used as the first dispersant. A problem arose where the viscosity of the dispersion increased by more than 20 times (at 2.5 / s) due to the formation of many hydrogen bonds between the first and second dispersants.

[0123] The dispersion in Comparative Example 4 was the same as the dispersion in Example 6, except that PVP-2 was used as the first dispersant. In this case, a problem arose in which the viscosity of the dispersion increased by more than 20 times (at 2.5 / s) due to the formation of many hydrogen bonds between the first and second dispersants.

[0124] To add elemental sulfur to the dispersion, two methods can be used: one using sulfur-substituted PVP (Examples 1-6) and the other using sulfide salts (Example 7). Both methods significantly reduced the viscosity of the dispersion. Of these, the method using sulfur-substituted PVP was found to reduce viscosity more dramatically.

[0125] From the above results, it can be concluded that adding sulfur to a carbon nanotube dispersion significantly reduces the viscosity of the dispersion.

Claims

1. A carbon nanotube, a first dispersant containing an amide group, a second dispersant containing at least one functional group selected from the group consisting of a hydroxyl group and a carboxyl group, and sulfur derived from the first dispersant, Some or all of the first dispersant is substituted with sulfur, A carbon nanotube dispersion in which the aforementioned sulfur element is contained in an amount of 0.01 to 10% by weight relative to the total weight of the solids in the dispersion.

2. The dispersion according to claim 1, wherein the content of the sulfur element is 0.01% to 20% relative to the total content of oxygen (O) and nitrogen (N), based on the total weight of the solids in the dispersion.

3. The dispersion according to claim 1, wherein the proportion of the first dispersant substituted with sulfur in the first dispersant is 10 to 100 mol%.

4. The first dispersant, as described above, exhibits a Fourier transform infrared (FTIR) spectrum of 1,140–1,180 cm⁻¹. －１ The second peak, and 1,180–1,220 cm －１ The dispersion according to claim 1, having at least one peak selected from the group consisting of a third peak.

5. The dispersion according to claim 1, wherein the first dispersant is polyvinylpyrrolidone, polyesteramide, polycarboxylamide, polyamidoamine, thioamidoamine, water-soluble nylon, or a combination thereof.

6. The dispersion according to claim 1, wherein the second dispersant contains an aromatic ring.

7. The dispersion according to claim 1, wherein the first dispersant and the second dispersant are contained in a weight ratio of 1:10 to 10:

1.

8. The carbon nanotubes have a BET specific surface area of ​​10 to 5,000 m². ２ The dispersion according to claim 1, having / g.

9. The dispersion according to claim 1, wherein the carbon nanotubes have an average particle size (D50) of 0.1 to 20 μm.

10. The method involves mixing a carbon nanotube, a first dispersant containing an amide group, and a second dispersant containing at least one functional group selected from the group consisting of a hydroxyl group and a carboxyl group. A method for producing a carbon nanotube dispersion according to any one of claims 1 to 9, wherein part or all of the first dispersant is substituted with sulfur.

11. An electrode slurry composition comprising an electrode active material, a binder, and a carbon nanotube dispersion according to any one of claims 1 to 9.

12. An electrode comprising an electrode active material layer formed from the electrode slurry composition according to claim 11.

13. The electrode according to claim 12, wherein the electrode is a negative electrode.

14. A secondary battery comprising the electrode described in claim 12.

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